1. Field of the Invention
The invention relates to grease compositions, and especially to such compositions containing inhibitors that suppress the formation of nitrosamines.
2. Discussion of the Prior Art
Grease compositions are generally used in environments where water, in minute or substantial quantity, is present. By way of illustration, grease compositions are required for military and naval use, as on the decks of navy and marine vessels, water pumps, mining machinery, steel and paper mills, food processing, and oil-well drilling operations. While the compositions provide lubricating value, they often fail to protect the metal parts with which they are in contact from rust formation. Required, then, are grease compositions that provide excellent lubrication in the presence of moisture and that inhibit rust formation.
Much progress has been made in fortifying grease compositions with rust inhibitors. Particularly effective in this regard is sodium nitrite. However, substantial concentrations of this salt are required to provide satisfactory inhibition and, with such concentrations, there may be a material loss of oxidation stability of the compositions. Therefore, many grease compositions also contain amines or products derived from amines as antioxidants. It is known that such a combination (i.e. nitrite plus amine) produces N-nitrosamines in lubrication environments. These have been found to be carcinogenic, and considerable effort has been put forth to discover combinations which do not produce nitrosamines. However, since the nitrites are among the most effective rust inhibitors for greases, many specifications have been built around these. Therefore, the continued use of nitrites is economically desirable, so the present inhibitor combination was developed to allow this.
Applicants know of no art teaching the use of the inhibitor combination of this invention in greases. However, the USDA has recommended that bacon containing sodium nitrite be inhibited against nitrosamine formation with a combination of sodium erythorbate (isoascorbate) and sodium ascorbate (see the Sept. 11, 1978 issue of Chemical and Engineering News, page 18).